Experimental study of the characteristics of the flow in the first rows of tube banks

Abstract

In the present work, the flow through tube banks is studied in order to understand the random and transient behavior of the instabilities and phenomena that occur in the first rows of tube banks and propagates to its interior. The study is performed using hot wire anemometry in an aerodynamic channel and flow visualizations in a water channel. Three tube banks with square arrangement and pitch-to-diameter ratios of 1.26, 1.4 and 1.6 were studied. The Reynolds number range for the velocities measurements, computed with the tube diameter and the flow velocity in the narrow gap between tubes, was 7-8x10 4. Continuous and discrete wavelets analyses were applied to decompose the velocity results, thus allowing the analysis of phenomena in a time-frequency domain. Visualizations in a water channel were made, using a dye injection directly in the flow, in order to help the understanding about the phenomena found. A tube bank with a square arrangement and 1.26 pitch-to-diameter ratio was used, and the experiments were performed in a Reynolds number range of 3-4x10 4. The main results show the presence of instabilities generated from the second row of the tube bank, which propagates to the interior of the bank, generating a behavior where the three orthogonal components of the flow are equally important. The three-dimensional behavior of the flow is responsible for a redistribution of mass inside of the bank of tubes that leads to velocity values and Strouhal numbers not expected for the studied geometry.

Surface pressure survey in a parallel triangular tube array

“…It is possible that flow instability was occurring at those velocities but it was not as pronounced as in the other cases and was masked by turbulence. Olinto et al (2009) reported that the bi-modal jet switching did not occur in water flow, but did in air flows at the same Reynolds number, but at higher flow velocity. So, an alternative explanation for an absence of jet switching at low velocities in this study, might be that there is some minimum flow velocity (i.e.…”

Finite mixture model applied in the analysis of a turbulent bistable flow on two parallel circular cylinders

“…Olinto et al (2006) determined by means of wavelet analysis of the results of hot wire experiments the presence of a biased and bistable flow mode in in-line tube banks and compared to the flow on two cylinders placed side-by-side. Further measurements together with flow visualizations in a water channel identified a phenomenon of random change in the flow mode, characterized by the presence of transversal components to the main flow that lead to the generation of a three dimensional behavior similar to the bistable flow that occurs in the flow on two tubes placed side by side, with the same scale to that of the channel (Olinto et al, 2009).…”

“…Wavelet analysis is a useful tool for the study of transient turbulent signals (Indrusiak et al, 2005;Olinto et al, 2009), and especially for the switching phenomenon in two side-by-side cylinders (Alam et al, 2003;Alam and Sakamoto, 2005). The use of wavelets together with flow visualizations can enhance the study of fluid flow phenomena in laboratory conditions.…”

Wymiana ciepła i wizualizacja przepływu dwufazowego w przestrzeni międzyrurowej

“…W zależności od wielkości strumieni doprowadzanych faz, ich właściwości fizykochemicznych i(lub) parametrów wrzenia formują się różne struktury przepływu. Duża liczba nowo wydawanych publikacji z tego zakresu pokazuje, że badania przepływu dwufazowego są wciąż w kręgu zainteresowań badaczy [2][3][4]. Jest to również spowodowane faktem, że pomimo wielu badań nad strukturami przepływu dwufazowego ich charakter nie został jeszcze w pełni poznany.…”